I'm worried that our new boy cat isn't very happy with us. Since we let him and his sister out two days ago the boy cat has mostly been home only for food.
What can I do to make him feel more at home? And what should I do next time he comes back? Should I keep him locked in the house for a few hours or days?
We adopted him and his sister three weeks ago through Blue Cross. They are eight years old and they are lovely cats. They've been sitting on our laps and sleeping on our bed. 
However we have two toddlers and the boy cat doesn't like being around them. He's been hiding under the bed a lot or staying in the cat bed they came in. He's generally waited until the children are safely asleep before coming out to explore the house.
I was hoping that once the cats could come and go as they pleased that the boy cat would feel less anxious as he could escape through the cat flap whenever he wanted. But it looks like he has decided he is just better off outdoors all the time.
He went out yesterday morning, we saw him in the garden twice during the day and he finally came in to eat at breakfast time today. His sister sniffed him, then hissed at him and whacked him over the head and soon after that he went off back out!
He did go into the study this morning where he had been napping on a chair sometimes. Unfortunately my husband has now moved that chair (grrr).